The invention relates to cursors, digitizing pens, mouse input devices utilized for inputting or and mouse input devides utilized for inputting or digitizing data or for inputting mouse commands to a computer, and more particularly to a four button cursor and method of operation.
The above-referenced parent application describes a cordless pen that may be utilized to digitize points lying along the surface of a digitizing tablet and also to input mouse commands via the tablet into a computer. The tubular structure of the cordless pen allows a cylindrical conductor to function as a relatively high capacitance virtual ground plane which cannot transmit error-causing electrostatic signals to the digitizing tablet. A relatively low capacitance conductive stylus tip protrudes from an open end of the cylindrical virtual ground plane and produces high intensity electrostatic signals that are scanned and precisely located by the digitizing tablet. The parent application explains at length why the ground plane capacitance must be large relative to the stylus capacitance. While the device has been very successful commercially, there are applications in which it would be desirable to have a "cursor" unit for digitizing points on a document resting on a digitizer surface, wherein the cursor rests on and is slid on the surface to be digitized, and has a cross hair that an operator can easily visually align with points to be digitized, and can conveniently actuate various control buttons to transmit various cursor commands to a computer via the digitizing tablet. Such a cursor unit would not be as subject to tilting as a typical digitizing pen, and could be more rapidly and precisely aligned with points to be digitized. Such a cursor unit thus would be very useful where a large number of points of a document need to be digitized. It also would be beneficial if such a cursor unit could be cordless, just as the cordless pen described in the above-referenced parent application has proven to be very convenient. However, the tubular conductor that functioned as effectively as a virtual ground plane in the above-described cordless pen is not readily adaptable to a cordless cursor of the above-described type. Therefore, it would be very convenient if the capacitance of the body of the person operating the cursor could be utilized as a ground plane capacitance. However, this technique presents a serious problem in the design of such a cursor unit, because the cursor typically will be left resting on the digitizing surface when an operator momentarily removes his or her hand from it. For example, when a operator initially grasps the cursor unit, there will be a large increase in the ground plane capacitance. Similarly, when the cursor operator releases the cursor unit, there will be a large decrease in the ground plane capacitance. When the net ground plane capacitance undergoes the decrease, the relatively small capacitance internal ground plane of the cursor will begin acting as an antenna, transmitting signals that are scanned by the digitizing tablet along with the signals being radiated by the antenna, producing errors in the digitized data.
A voltage doubling circuit is described in the above-referenced parent application for boosting the voltage generated by the batteries in the cordless pen. Although that circuit operates well, it would be desirable to provide an even more effective voltage booster circuit, so that scanning by the digitizing tablet can be more accurate.